This invention relates to improvements in the production of chlorine by catalytic oxidation of hydrogen chloride. This invention relates more particularly to improvements in the manufacture of chlorine by the oxidation of hydrogen chloride containing small amounts of organic impurities and is particularly suitable for the production of chlorine from hydrogen chloride in the presence of a chloride of a metal having an atomic number of from 21 to 30 inclusive.
Hydrogen chloride is formed as a by-product in a number of important industrial processes such as the manufacture of freon gases, vinyl chloride monomer, tolylene diisocyanate and the like. However, such hydrogen chloride often contains organic impurities, complicating its reuse, or ultimate disposal. Over the years a number of processes have been proposed for recovery of chlorine from the hydrogen chloride by oxidation with an oxygen-containing gas. U.S. Pat. No. 2,855,279 relates a process for oxidizing liquid hydrochloric acid using a nitrogen dioxide type catalyst wherein nitrogen dioxide and moisture are removed from the reaction product by scrubbing with sulfuric acid. Unreacted oxygen is then separated by venting after absorption of the chlorine product into carbon tetrachloride at 40-500 psig. The chlorine is recovered in gaseous form by release of the pressure to 10-30 psig. The carbon tetrachloride is then recompressed and recycled to again absorb chlorine. Other processes are described, for example, in U.S. Pat. Nos. 2,299,427; 2,448,255, 2,542,961; 2,644,846; 2,746,844; 3,201,201; 3,210,158; 3,242,648; and 3,260,678.
As is known, for example, from U.S. Pat. No. 3,233,978 organic impurities in the hydrogen chloride being oxidatively converted to chlorine are themselves typically converted to halohydrocarbons such as carbon tetrachloride and hexachloroethane. The latter compound is a particular problem owing to its high melting point of 187.degree. C. (368.degree. F.) and its tendency when condensed, particularly into aqueous systems, to adhere to and foul conventional solids separation equipment, heat exchange equipment and the like. This tendency for fouling is disruptive of efficient continuous operations. Thus it is readily apparent that there exists a need for an improved process to efficiently convert hydrogen chloride containing impurities to chlorine, while avoiding disruptive fouling during operations.
The improvements of the invention provides such a process.